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Diode Clamped Emitter Follower Circuit

IP.com Disclosure Number: IPCOM000084817D
Original Publication Date: 1976-Jan-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Coullahan, JP: AUTHOR [+2]

Abstract

To drive a distributed heavily loaded terminated transmission line between chips or modules, a terminated line driver may be employed. The receiver chip, or module, has an off-chip receive circuit that switches around the Vbb power supply.

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Diode Clamped Emitter Follower Circuit

To drive a distributed heavily loaded terminated transmission line between chips or modules, a terminated line driver may be employed. The receiver chip, or module, has an off-chip receive circuit that switches around the Vbb power supply.

When switching from the most positive uplevel (MPUL) of the driver circuit to the least negative threshold of the receiver circuit, the first incident switching (to minimize delay across boundaries) of the receiver circuit is not achieved. This is due to the reduction of effective impedance of the transmission line (Zo < R terminator), due to heavy loading which reduces the initial voltage swing. The switching on first incidence is further hampered by the lack of tracking between driver uplevel and the receiver threshold.

By clamping the base of the emitter-follower to a lower uplevel, the voltage swing required to switch the receiver is reduced. As depicted in the drawing, this may be accomplished by serially connecting two diodes in series between the base of the emitter-follower transistor and the Vbb power supply. In so doing, the Vbb power supply of the driver and receiver track, to achieve first incident switching of the receiver, and provide the proper voltage swing.

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